Recording media having protective overcoats of highly tetrahedral amorphous carbon and methods for their production

ABSTRACT

The invention provides systems and methods for the deposition of an improved diamond-like carbon material, particularly for the production of magnetic recording media. The diamond-like carbon material of the present invention is highly tetrahedral, that is, it features a large number of the sp 3  carbon-carbon bonds which are found within a diamond crystal lattice. The material is also amorphous, providing a combination of short-range order with long-range disorder, and can be deposited as films which are ultrasmooth and continuous at thicknesses substantially lower than known amorphous carbon coating materials. The carbon protective coatings of the present invention will often be hydrogenated. In a preferred method for depositing of these materials, capacitive coupling forms a highly uniform, selectively energized stream of ions from a dense, inductively ionized plasma. Such inductive ionization is enhanced by a relatively slow moving (or “quasi-static”) magnetic field, which promotes resonant ionization and ion beam homogenization.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of and claims the benefit ofpriority from U.S. patent application Ser. No. 09/648,341, filed Aug.25, 2000, which is a continuation of U.S. patent application Ser. No.09/165,513, filed Oct. 2, 1998, which is a divisional of U.S. patentapplication Ser. No. 08/761,336, now U.S. Pat. No. 5,858,477, filed Dec.10, 1996, which is a continuation-in-part of and claims priority fromU.S. Provisional Patent Applications Serial No. 60/018,793, filed May31, 1996, and Serial No. 60/018,746, filed May 31, 1996, the fulldisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to thin films and methodsfor their deposition, and more particularly, provides diamond-likefilms, plasma beam deposition systems, and methods useful for productionof diamond-like protective overcoats on magnetic recording media andother industrial applications.

[0004] In recent years, there has been considerable interest in thedeposition of a group of materials referred to as diamond-like carbon.Diamond-like carbon can generally be defined as a metastable, highdensity form of amorphous carbon. Diamond- like carbon is valued for itshigh mechanical hardness, low friction, optical transparency, andchemical inertness.

[0005] Deposition of diamond-like carbon films often involves chemicalvapor deposition techniques, the deposition processes often being plasmaenhanced. Known diamond-like films often include carbon with hydrogen,fluorine, or some other agent. The durability and advantageouselectrical properties of diamond-like carbon films have led to numerousproposals to apply these films to semiconductors, optics, and a widevariety of other industrial uses. Unfortunately, the cost and complexityof providing these advantageous diamond-like carbon films using knownchemical vapor deposition processes has somewhat limited their use.Furthermore, while a wide variety of diamond-like carbon coating filmshave been deposited in laboratories, many of these films have been foundto have less than ideal material characteristics.

[0006] A very different form of amorphous carbon is generally applied asa protective overcoat for magnetic recording media. Magnetic recordingdisks generally comprise a substrate having a magnetic layer and anumber of underlayers and overlayers deposited thereon. The nature andcomposition of each layer is selected to provide the desired magneticrecording characteristics, as is generally recognized in the industry.

[0007] The information stored in magnetic recording media generallycomprises variations in the magnetic field of a thin film offerromagnetic material, such as a magnetic oxide or magnetic alloy.Usually, a protective layer is formed over the top of the magneticlayer, and a layer of lubricating material is deposited over theprotective layer. These protective and lubricating layers combine toincrease the reliability and durability of the magnetic recording mediaby limiting friction and erosion of the magnetic recording layer.Sputtered amorphous carbon films have gained widespread usage asprotective overcoats for rigid magnetic recording disks.

[0008] Sputtered amorphous carbon overcoats have been shown to provide ahigh degree of wear protection with a relatively thin protective layer.Magnetic recording disk structures including sputtered amorphous carbonhave been very successful and allow for quite high recording densities.As with all successes, however, it is presently desired to providemagnetic recording disks having even higher recording densities.

[0009] Recording densities can generally be improved by reducing thespacing between the recording transducer, called the read/write head,and the magnetic layer of the magnetic recording disk (or morespecifically, between the read/write head and the middle of the magneticlayer). In modem magnetic recording systems, the read/write head oftenglides over the recording surface on an air bearing, a layer of airwhich moves with the rotating disk. To minimize frictional contactbetween the rotating disk and the read/write head, the disks surface isgenerally rougher (and the glide height therefore higher) than wouldotherwise be ideal for high density magnetic recording. Even if thisglide height is reduced (or eliminated), the read/write head will beseparated from the recording layer by the protective amorphous carbonovercoat. This protective layer alone may, to provide the desired medialife, limit the areal density of the media. Generally, overcoat layerthicknesses are dictated by durability and continuity limitations.Sputtered carbon frequently becomes discontinuous at thicknesses belowabout 50Å. Thus, the durability requirements of rigid magnetic recordingmedia generally dictate that the distance between the read/write headand the magnetic recording layer be maintained, even though this limitsthe areal density of the magnetic recording media.

[0010] It has previously been proposed to utilize known chemical vapordeposition techniques to deposit a variety of diamond-like carbonmaterials for use as protective coatings for flexible magnetic recordingtapes and magnetic recording heads. Unfortunately, known methods forchemical vapor deposition of diamond-like materials, including plasmaenhanced methods, generally subject the substrate to temperatures ofover 500° C., which is deleterious for most magnetic disk substrates.Therefore, these known diamond-like carbon films do provide relativelygood hardness and frictional properties, they have found littlepractical application within the field of rigid magnetic recordingmedia, in which sputtered amorphous carbon protective overcoats areoverwhelmingly dominant.

[0011] For these reasons, it would be beneficial to provide improvedmagnetic protective overcoats with improved read/write head frictionaland glide characteristics (generally called stiction) for recordingmedia. Preferably, such an improved overcoat will provide durability andreliability without having to resort to the density-limiting glideheights and/or protective overcoat thickness of known rigid magneticrecording media, and without subjecting the media substrates toexcessive temperatures.

[0012] It would also be desirable to provide improved diamond-likecarbon materials and methods for their deposition. It would beparticularly desirable if such materials and methods could be utilizedfor practical rigid magnetic recording media with reduced spacingbetween the read/write head and the magnetic recording layer, ideally byproviding a flatter, smoother, and thinner protective coating whichmaintained or even enhanced the durability of the total recording mediastructure. It would also be advantageous to provide alternative methodsand systems for depositing such protective layers, for use in theproduction of magnetic recording media, as well as integrated circuits,optics, machine tools, and a wide variety of additional industrialapplications.

[0013] 2. Description of the Background Art

[0014] U.S. Pat. No.5,182,132 describes magnetic recording media havinga diamond-like carbon film deposited with alternating circuit plasmaenhanced chemical vapor deposition methods. U.S. Pat. No. 5,462,784describes a fluorinated diamond-like carbon protective coating formagnetic recording media devices. European Patent Application 700,033describes a side-mounted thin film magnetic head having a protectivelayer of diamond-like carbon. European Patent Application No. 595,564describes a magnetic recording media having a diamond-like protectivefilm which consists of carbon and hydrogen.

[0015] U.S. Pat. No. 5,156,703 describes a method for the surfacetreatment of semiconductors by particle bombardment, the method makinguse of a capacitively coupled extraction grid to produce an electricallyneutral stream of plasma. V. S. Veerasamy et al. described theproperties of tetrahedral amorphous carbon deposited with a filteredcathodic vacuum arc in Solid-State Electronics, vol. 37, pp. 319-326(1994). The recent progress in filtered vacuum arc deposition wasreviewed by R. L. Boxman in a paper presented at the InternationalConference of Metallurgical Coatings and Thin Films located at San Diegoin April of 1996. Electron cyclotron wave resonances in low pressureplasmas with a superimposed static magnetic field were described byProfessor Oechsner in Plasma Physics, vol. 15, pp. 835-844 (1974).

SUMMARY OF THE INVENTION

[0016] The present invention provides systems and methods for thedeposition of an improved diamond-like carbon material, particularly forthe production of magnetic recording media. The diamond-like carbonmaterial of the present invention is highly tetrahedral, that is, itfeatures a large number of the sp³ carbon-carbon bonds which are foundwithin a diamond crystal lattice. The material is also amorphous,providing a combination of short-range order with long-range disorder,and can be deposited as films which are ultrasmooth and continuous(pin-hole free) at thicknesses substantially lower than known amorphouscarbon coating materials. The carbon protective coatings of the presentinvention will often be hydrogenated, generally providing asignificantly higher percentage of carbon carbon sp³ bonds than knownhydrogenated amorphous diamond-like carbon coatings having similarcompositions, and may optionally be nitrogenated. In a preferred methodfor depositing of these materials, capacitive coupling forms a highlyuniform, selectively energized stream of ions from a dense, inductivelyionized plasma. Such inductive ionization is enhanced by a relativelyslow moving (or “quasi-static”) magnetic field, which promotes resonantionization and ion beam homogenization. Clearly, the materials, systems,and methods of the present invention will find applications not only inthe field of magnetic recording media and related devices, but also inintegrated circuit fabrication, optics, machine tool coatings, and awide variety of film deposition and etching applications.

[0017] In a first aspect, the present invention provides a method forproducing magnetic recording media, the method comprising forming amagnetic layer over a substrate, and ionizing a source material so as toform a plasma containing carbon ions. The carbon ions are energized toform a stream from the plasma toward the substrate, so that carbon fromthe ions is deposited on the substrate. The ions impact with an energywhich promotes formation of sp³ carbon-carbon bonds. Advantageously,such a method can form a highly tetrahedral amorphous carbon protectivelayer, generally having more than about 15% sp³ carbon-carbon bonds.Generally, the impact energy of the energetic carbon ions is within apre-determined range to promote formation of the desired latticestructure, the bonds apparently being formed at least in part bysubplantation. Preferably, each carbon ion impacts with an energy ofbetween about 100 and 120eV. In many embodiments, the resulting highlytetrahedral amorphous carbon protective layer includes more than about35% sp³ carbon-carbon bonds, with particularly preferred methodsproducing more than about 70% sp³ carbon carbon bonds.

[0018] Generally, the stream will be primarily composed of ions having auniform weight, and the impact energy will preferably be substantiallyuniform. In some embodiments, this uniformity is promoted throughfiltering of the ion stream. In such cases, the energizing stepgenerally comprises striking a plasma using a solid cathodic arc ofcarbon source material. Alternatively, the stream will be energized byapplying an alternating potential between a coupling electrode and anextraction grid so as to self-bias the plasma relative to the extractiongrid through capacitive coupling, thereby extracting the ion streamthrough the grid. Hydrogen and/or nitrogen may also be included, both inthe ion stream and the protective layer.

[0019] In another aspect, the present invention provides magneticrecording media comprising a substrate, a magnetic layer disposed overthe substrate, and a protective layer disposed over the magnetic layer.The protective layer comprises a highly tetrahedral amorphous carbon,generally having more than about 15% sp³ carbon-carbon bonds.Preferably, these bonds are formed at least in part by directing anenergetic stream of carbon ions onto the substrate. In many embodiments,the protective layer includes more than about 35% sp³ carbon carbonbonds, with particularly preferred embodiments including more than about70% sp³ carbon carbon bonds. Such protective layers are ultrasmooth andcontinuous at thicknesses of less than about 75 Å, and will providedurable recording media even at thicknesses of less than about 50 Å.Furthermore, the hardness and tribological performance of these denseprotective materials may allow highly durable recording media with arealrecording densities of over 1 gigabyte per square inch with reducedread/write head glide heights of lower than about 1μ″, optionally withina near-contact or continuous contact recording systems.

[0020] In another aspect, the present invention provides a method forenhancing an ion beam, the ion beam produced by confining a plasmawithin a plasma volume, inductively ionizing the plasma, and forming astream of ions from within the plasma volume by capacitive coupling. Themethod comprises moving a magnetic field through the plasma to promoteresonant inductive ionization, preferably by sequentially energizingeach of a plurality of coils disposed radially about the plasma volume.

[0021] In another aspect, the present invention provides an inductiveionization system for use with an ion-beam source. The source includesan antenna disposed about a plasma volume for inductively ionizing aplasma therein. A coupling electrode is exposed to the plasma volume andan extraction electrode is disposed over an opening of the plasmavolume, so that the extraction electrode is capable of expelling ions ofthe plasma through the grid by capacitive coupling. The system comprisesat least one coil disposed adjacent the plasma volume capable ofapplying a transverse magnetic field to the plasma volume so as topromote resonant inductive ionization by the antenna. The magnetic fieldcan be moved through the plasma container to homogenize the expelled ionstream. This movement of the magnetic field, which is optionallyprovided by selectively energizing coils radially disposed about theplasma volume, may also further densify the plasma by promoting particlecollisions through a churning or mixing effect.

[0022] In another aspect, the present invention provides a diamond-likematerial comprising carbon in the range between about 72 and 92 atomicpercent, and hydrogen in the range between about 8 and 18 atomicpercent. The material is amorphous, and between about 15 and 85 percentof carbon-carbon bonds are sp^(3 bonds. Generally, sp) ³ bond formationwill be promoted with subplantation using ion-beam deposition from aplasma beam source, so that the number of such bonds will be higher thanknown materials having similar compositions. Hence, the highlytetrahedral amorphous carbon and hydrogenated carbon of the presentinvention will have fewer polymer-like hydrogen chains, and willgenerally exhibit enhanced thermal and mechanical stability.

[0023] In another aspect, the present invention provides a method fordeposition of highly tetrahedral amorphous carbon over a substrate, themethod comprising ionizing a source material to form a plasma andconfining the plasma within a plasma volume. The plasma is capacitivelycoupled to form a stream flowing outwardly from within the plasmavolume.

[0024] The stream includes carbon ions from the plasma and is directedonto the substrate. Advantageously, such a method allows deposition ofcarbon ions of uniform size with a uniform energy, and allows tailoringof the energetic carbon ions to specifically promote sp³ bonding throughsubplantation. The source material typically comprises a gas having asubstantially coherent dissociation energy spectra, the source gasideally comprising acetylene. Preferably, the ions strike the substratewith an impact energy of between about 57 and 130 eV for each carbonatom, ideally being between about 80 and 120 eV each.

[0025] In another aspect, the present invention provides an ion-beamsource comprising a container defining a plasma confinement volume. Thecontainer has an opening, and an antenna is disposed about the plasmavolume so that application of a first alternating potential to theantenna is capable of inductively ionizing a plasma therein. A couplingelectrode is electrically coupled to the plasma volume and an extractionelectrode is disposed over the opening of the container. The extractionelectrode has a surface area which is substantially less than thecoupling electrode surface, so that application of a second alternatingpotential between the coupling electrode and the extraction electrode iscapable of expelling ions of the plasma through the grid. Preferably, atleast one coil is disposed adjacent the container, and is capable ofapplying a transverse magnetic field to the plasma volume, therebypromoting highly efficient inductive ionization resonance by theantenna. Ideally, the magnetic field can be moved through the plasmacontainer to homogenize the expelled ion stream. This movement of themagnetic field, which is optionally provided by selectively energizingcoils radially disposed about the plasma confinement volume, may furtherdensity the plasma by promoting particle collisions with a churning ormixing effect. In yet another aspect, the present invention provides anion-beam source comprising plasma containment means for confining aplasma within a plasma volume. Inductive ionization means inductivelycouples a first alternating current with the plasma so as to ionize theplasma within the plasma volume. A moving magnetic field generationmeans provides resonant densification and homogenization of the ionizedplasma within the plasma volume. Ion extraction means forms a stream ofions out from the plasma volume.

[0026] In another aspect, the present invention provides a method forproducing an ion beam, the method comprising confining a plasma within aplasma volume, inductively ionizing the plasma, and forming a stream ofions from within the plasma volume by capacitively coupling the plasmawith an extraction grid. This capacitive coupling self- biases theplasma relative to the grid, and can be used to produce a quasi-neutralplasma stream. Generally, a transverse magnetic field is applied todensity the plasma by promoting resonant inductive ionization. Ideally,the magnetic field is moved through the plasma volume to homogenize theplasma and plasma stream.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 is a cross-sectional view of a magnetic recording diskincluding the tetrahedral amorphous hydrogenated carbon protective layerof the present invention.

[0028]FIGS. 1A and B illustrate the effects of nitrogen doping on thetetrahedral amorphous hydrogenated carbon of the present invention.

[0029]FIG. 2 schematically illustrates a method for depositing thehighly tetrahedral amorphous hydrogenated carbon over the disk of FIG.1, and also shows a hybrid inductive/capacitive plasma beam sourceaccording to the principles of the present invention.

[0030]FIG. 2A is a cross-sectional view of the hybrid source of FIG. 2,showing the inductive ionization antenna and quasi-static magnetic fieldgenerating coils which density and homogenize the plasma.

[0031]FIG. 3A illustrates an alternative method and system fordepositing highly tetrahedral amorphous hydrogenated carbon over thedisk of FIG. 1 using an acetylene plasma from a plasma beam source.

[0032]FIGS. 3B and C illustrate capacitive coupling of the plasma toextract a stream of ions when using the plasma beam source of FIG. 3A.

[0033]FIG. 3D illustrates an alternative embodiment of a plasma beamsource, in which the effective area of the coupling electrode can bevaried to provide further control over the ion density and ion energy.

[0034]FIGS. 3E and F illustrate operating characteristics of plasma beamsources for deposition of diamond-like carbon.

[0035]FIGS. 4A and B illustrate known resonant inductive ionization of aplasma with a fixed magnetic field.

[0036]FIGS. 4C and D explain densification of the plasma provided byElectron Cyclotron Wave Resonance.

[0037]FIG. 5 illustrates an alternative method and deposition system forproducing the recording disk of FIG. 1, which system relies upon afiltered cathodic arc for deposition of the highly tetrahedral amorphoushydrogenated carbon material of the present invention.

[0038] FIGS. 6A-8 show experimental data, as described in detail in theexperimental section.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

[0039] Referring now to FIG. 1, a rigid magnetic recording disk 2comprises a non-magnetic disk substrate 10, typically composed of analuminum alloy, glass, ceramic, a glass-ceramic composite, carbon,carbon-ceramic composite, or the like. An amorphous nickel phosphous(Ni—P) layer 12 is formed over each surface of the disk substrate 10,typically by plating. The Ni—P layer is hard, and imparts rigidity tothe aluminum alloy substrate. A chromium ground layer 14 is formed overNi—P layer 12, typically by sputtering, and a magnetic layer 16 isformed over the ground layer 14. Please note that these layers are shownschematically only, as NiP layer 12 will typically be much thicker thanthe other layers.

[0040] The magnetic layer 16 comprises a thin film of a ferromagneticmaterial, such as a magnetic oxide or magnetic alloy. Magnetic layer 16is typically sputtered over ground layer 14 in a conventional manner.The magnetic layer will often be composed of a cobalt alloy, such as aCoCrTaPtB, CoCrPtB, CoCrTa, CoPtCr, CoNiCr, CoCrTaXY (X and Y beingselected from Pt, Ni, W, B, or other elements) or the like. The magneticlayer may be formed as a single layer, or may comprise two or morelayers formed over one another. The thickness of magnetic layer 16 istypically in the range from about 200 Å to 800 Å.

[0041] Of particular importance to the present invention is a protectivelayer 18 which is formed over the magnetic layer. The protective layer18 of the present invention will generally comprise a highly tetrahedralamorphous carbon, typically having more than about 15% sp³ carbon-carbonbonds, preferably being more than about 35% sp³ carbon-carbon bonds, andideally being over about 70% sp³ carbon-carbon bonds, as measured usingRaman fingerprinting and electron energy loss spectroscopy. Along withcarbon, protective layer 18 may also include hydrogen, generally formingin the range between about 2 and 30 atomic percent of the protectivematerial, preferably being between 8 and 18 atomic percent. Aconventional lubricating layer 20 is disposed over the protective layer.

[0042] Although hydrogen is known to increase the percentage of sp³bonding of diamond-like carbon produced by known chemical vapordeposition processes, protective layer 18 will generally includesignificantly less hydrogen than comparable known diamond-like films.This compositional difference may be explained in part by the formationof sp³ bonds through subplantation of the energetic carbon ions duringdeposition. Effectively, the energetic ions deposited using the methodsdescribed hereinbelow impact on the growing film surface, and are driveninto the film so as to cause densification. This process may alsoexplain why the protective layer of the present invention includes ahigher percentage of quaternary carbon sites (sp³ carbon sites with nohydrogen neighbors) and greater hardness than known alternativeamorphous carbon materials.

[0043] The microstructure of conventional hydrogenated amorphous carbonsincludes polymer-like hydrocarbon chains. Although hydrogen enhances theformation of tetrahedrally bonded carbon atoms, above a certainthreshold value of hydrogen content, carbon films become polymeric andhence lose their protective properties. Through subplantation, thematerials of the present invention overcome this limitation. Assubplantation promotes formation of sp³ bonds without relying onadditional hydrogen content alone, polymerization can be avoided. Thisrepresents a substantial advantage over known, more highly hydrogenateddiamond-like carbon materials, in which polymerization significantlylimits both thermal and mechanical stability. In contrast, thecarbon-carbon sp³ bonds of the materials of the present invention willgenerally be stable up to temperatures of about 700° C., so that anenhanced percentage of sp³ bonds with a low hydrogen content representsa significant advantage.

[0044] Optionally, the films of the present invention may also benitrogenated. In contrast to known hydrogenated carbon, the electricalconductivity of the present highly tetrahedral amorphous carbon can becontrollably varied over a wide range by the selective incorporation ofnitrogen during the C₂H₂ plasma beam deposition process describedhereinbelow. Advantageously, this variation will be provided withoutsignificantly varying the structural properties of the film. Withconventional hydrogenated carbon, nitrogen incorporation may be relatedto the formation of sp² bonds. This will be evident by variations in themechanical and optical properties of the films deposited, for whichharness and optical gap will decrease with nitrogen content. With thepresent film materials and deposition methods, a classic doping effectis observed, in which electrical conductivity can be controllably variedby as much as 5 orders of magnitude or more, as is shown in FIGS. 1A andB. Doping can be provided by varying nitrogen pressure within a plasmavolume of an acetylene fed plasma beam source, typically to providefilms having from about 4 to about 30 atomic percent nitrogen. Thisdoping effect of highly tetrahedral amorphous carbon and hydrogenatedcarbon will find particular application for the fabrication ofintegrated circuits and the like.

[0045] The highly tetrahedral amorphous carbon materials of the presentinvention also provide a number of advantages over known protectivelayers for recording media. The bond structure of this material providesphysical properties approaching those of diamond, including a hardnessof over about 50 GPa, with certain species having hardness of up toabout 80 GPa. Furthermore, the present protective overcoats have highdensity, generally being over about 2.5 grams per cubic centimeter, andare also very chemically inert.

[0046] Of particular importance to recording media, these coatings aresmooth and continuous (pinhole-free) at very low thicknesses, andprovide a durable protective layer when deposited to a thickness of lessthan 75 Å, preferably being less than 50 Å thick. In fact, films of over150 Å may be more susceptible to delamination, and surface roughness mayincrease with thickness. The high mechanical hardness and low frictionsurfaces provided by these materials lead to enhanced tribologicalperformance, providing recording media which are highly tolerant to themechanical abrasion and contact start-stop demands of modem recordingmedia systems, and allowing increased areal density through reducedseparation between the read/write and the magnetic layer. Thisseparation may be reduced by either a reduction in the protective layerthickness, or by a reduction in head glide height, and preferably by areduction in both. Protective layer 18 is generally in the range betweenabout 30 Å and 70 Å, which will allow the disk to meet recording mediaindustry durability and stiction test requirements.

[0047] The composition and characterization of the protective film ofthe present invention are highly dependent on the deposition method, andin particular, depend strongly on the energy and uniformity of carbonions striking the deposition surface.

[0048] An exemplary system and method for depositing protective layer 18on rigid recording disk 2 will be described with reference to FIGS. 2and 2A. Hybrid ion beam source 30 generally includes an inductiveionization system 32, a quasi-static magnetic field system 34, and acapacitive ion beam extraction system 36.

[0049] In general terms, induction system 32 ionizes a plasma 38. Theenergy transfer between induction system 32 and plasma 38 is greatlyenhanced and homogenized by a transverse magnetic field generated byquasi-static field system 34. The deposition ions of plasma 38 areactually directed to recording disk 2 (or to any other substrate onwhich deposition is desired, or from which etching will be performed)using capacitive coupling system 36.

[0050] Although hybrid source 30 provides a particularly advantageoussystem for deposition of the protective coating 18, a variety ofalternative deposition systems may also be used. As a plasma beam sourcedeposition system shares a number of the features of hybrid source 30,but is simpler in operation, diamond-like carbon deposition using aplasma beam source 50 will be described with reference to FIGS. 3A-F,after which other aspects of hybrid source 30 will be explained in moredetail.

[0051] Referring now to FIG. 3A, the use of plasma beam source 50 forthe deposition of carbon will generally be described with reference todepositing protective layer 18 on magnetic recording media 2. As hasbeen mentioned above, these carbon deposition systems and methods willhave a wide variety of alternative uses, particularly in the areas ofintegrated circuits fabrication, optics, and machine tools.

[0052] Plasma beam source 50 includes a plasma container 52 whichdefines a plasma volume 54 therein. Container 52 is typically an 8 cmdiameter glass tube, or may alternatively comprise quartz or the like. Acoupling electrode 56 having a relatively large surface 58 here formsone end of the container. Alternatively, the coupling electrode may bedisposed within or external to the container, and may optionally extendaxially along the walls of the container. Regardless, coupling electrode56 is generally electrically coupled to the plasma, to a matchingnetwork 60, and to a radiofrequency coupling power supply 62. Plasmacoupling system 36 includes coupling electrode 56, the frequencygenerator and matching network 60, 62, and an extraction grid 64.Typically, the extraction grid will be grounded as shown.

[0053] As is explained more fully in U.S. Pat. Ser. No. 5,156,703, thefull disclosure of which is herein incorporated by reference, extractiongrid 64 has a much smaller surface area exposed to the plasma than thecoupling electrode 56. In operation, RF power, typically at about 13.56MHz, is supplied by the frequency generator through the matching networkand a capacitor to the coupling electrode. This frequency will often beset by government regulations, and may alternatively be about 27.12 MHz,or some other multiple thereof. The extraction grid typically comprisesa graphite rim 66 defining an aperture, and tungsten filaments which aremaintained under tension. Hence, extraction grid 64 resists anydistortion due to thermal expansion. A number of alternative materialsmay be used in the filaments, the filament materials preferably having alow sputtering yield.

[0054] Generally, internal pressure within plasma volume 54 is reducedby removing gas through vacuum port 68. While the vacuum port is hereshown behind the grid, it will preferably be disposed between grid 64and disk 2. Advantageously, when a plasma is struck between the couplingelectrode and the extraction grid, the plasma shifts to a positive DCpotential with respect to the extraction grid, due to the relativemobility of the electrons as compared to the ions within the plasma.Specifically, the greater mobility of electrons than ions in the plasmacauses the plasma to form a sheath between itself and each electrode.The sheaths act as diodes, so that the plasma acquires a positive DCbias with respect to each electrode.

[0055] The total radiofrequency potential V₀ will be divided between thesheaths adjacent the powered electrode and the grounded electrode,according to their respective capacitances. As the extraction electrodeis grounded, the voltage of the plasma itself is given by the equation

V =V ₀ (C _(e) /(C _(g) +C _(e))) wherein C_(e) is the capacitance ofthe coupling electrode, while C_(g) is the capacitance of the extractiongrid.

[0056] Where the extraction electrode is grounded, this plasma voltagebiases the plasma relative to the grid, accelerating the ions throughthe extraction grid and toward the substrate. As can be determined fromthe above equation, the plasma beam source allows the biasing voltage tobe selectively controlled, providing a highly advantageous mechanism forcontrolling ion impact energy.

[0057] As capacitance varies inversely with area, the size of the biasvoltage at each electrode can be controlled by varying the electrodeareas. As the extraction grid has a much smaller area than the couplingelectrode, the biasing of the plasma relative to the coupling electrodeis relatively low, so that source 50 provides a fairly efficient use ofthe source gas material, which is generally provided through sourceinlet 70 adjacent coupling electrode 56. While some material will bedeposited on the container walls at higher power settings, use of theplasma beam source in an etching mode may allow self cleaning.

[0058] The relationship of electron current, ion current, and theradiofrequency potential is illustrated in FIG. 3B. A simplifiedelectrical diagram for analysis of the plasma, the extraction gridsheath, and the coupling grid sheath, is shown in FIG. 3C.

[0059] A still further aspect of the plasma beam source carbondeposition system and method of the present invention is illustrated inFIG. 3D. Plasma 74 is here contained within a hyperbolic magnetic fieldproduced by magnets 78. An axially movable coupling electrode 80 issupported by a movable ceramic pipe 82 which slides axially through aceramic end 84 of the plasma container vessel.

[0060] The magnetic confinement of the plasma allows the effective areaof coupling electrode 80 to be varied by moving the coupling electrodeaxially relative to the plasma. This allows the bias voltage (and hencethe ion energy) to be varied without changing the radiofrequency poweror the gas pressure. Alternatively, the ion saturation current density(deposition rate) and ion energy can be varied by changing theradiofrequency power and gas feed stock flow rate. The ion current andion energy distribution can be measured with a Faraday cup 86 in thesubstrate plane 88. FIG. 3E shows variations of ion current and mean ionenergy with electrode position D for a range of radiofrequency powers.

[0061] The ion energy depends on at least two factors: the accelerationpotential across the grid sheath, and the energy lost by collisionswithin the sheath. The effects of these factors are illustrated in FIG.3F.

[0062] The inset to FIG. 3F shows that the ion energy distribution ofthe plasma beam is quite sharp, with a width of approximately 5% aboutthe bias voltage. The sharpness apparently arises for at least tworeasons. First, ions lose little energy in the low plasma pressurethrough collisions within the sheath. Second, the sheath width variesinversely with the square root of pressure, so that the sheath is quitewide at low pressures. Where the ion transit time across the sheath islonger than the radiofrequency period, the ions may be accelerated bythe mean voltage rather than the instantaneous voltage. The ion energydistribution width is also found to vary linearly with pressure, whichindicates that the ion energy distribution width is controlled mainly byion collisions in and above the sheath.

[0063] The decomposition or dissociation of hydrocarbons in plasma 74depends strongly on the source gas, the operation pressure, and the gasflow rate. Usually, hydrocarbon plasmas exhibit a wide spectrum ofhydrocarbon radicals in an ionized and/or neutral state. The plasmacomposition depends on the various chemical pathways in the plasma, andthese depend on the plasma parameters such as electron temperature,electron density, and degree of ionization. As a result, a number ofdifferent ions may be present in the plasma, and the composition maychange markedly under different conditions, making uniform deposition ofhomogeneous hydrogenated carbon materials fairly problematic.

[0064] Work in connection with the present invention has shown thatacetylene provides a highly advantageous source gas because of itsrelatively simple dissociation pattern. The plasma decomposition of amolecule can be described in terms of electron-molecule (primary) andion-molecule (secondary) collisions, and their associated ratecoefficients or their related appearance potentials. Advantageously, thedissociation of acetylene is dominated by its ionization at anappearance potential of 11.2 eV. Acetylene may be unique among thehydrocarbons in having such a well-defined reaction path.

[0065] The ionic composition of a plasma beam produced using anacetylene source gas produces a mass spectra at various plasma pressureswhich are dominated by the C₂H₂ ⁺ ion and other hydrocarbon ions havingtwo carbon atoms, collectively referred to as the C₂ species. The nextmost significant ions are the C₄ ions, which have been found to decreasein intensity as the pressure is lowered, being below 5% if the pressureis maintained below 5 ×10 ⁻⁵ mbar. For these reasons, carbon depositionusing the plasma beam source and hybrid source of the present inventionis preferably performed using a feed stock which comprises acetylene.Optionally, N₂, NF₃, or some other nitrogen feedstock may also beincluded to provide nitrogenated films.

[0066] The particle flux or stream provided by a plasma beam depositionsystem or a hybrid deposition system will generally have a higher degreeof ionization than conventional deposition techniques. The formation ofcarbon-carbon sp³ bonds through the subplantation effect may only besignificant if sufficient ions are present in the particle stream.Preferably, at least 15% of the particles will comprise ions. In someembodiments, particularly at very low deposition pressures, thefilm-forming particle flux will comprise over 90% ions.

[0067] When depositing using a plasma beam source, the incident powerprovided to the coupling electrode will generally be between about 50and 700 watts, ideally being between about 200 and 300 watts. Whereopposite sides of a substrate will be simultaneously coated, two plasmabeam sources may be provided, preferably having independentradiofrequency generators which are phase-matched, ideally beingsynchronized in a master/slave configuration. Radiofrequency reflectedpower will generally be between about 5 and 70 watts, and should beminimized by selection of proper network elements.

[0068] The magnetic containment field coil nearest the substrate may beprovided with a current of between 1 and 8 amps, ideally being about 7amps. The outer field coil will have between one-half and 5 amps ofcurrent flowing therethrough, wherein the current is the reversepolarity of the inner coil current. Gas flow rates of from 5 sccm to 30sccm are sufficient to maintain the plasma, with the gas flow rateideally being about 18 scem. Igniting the plasma is facilitated byproviding an initial burst of between 40 and 50 sccm of N₂ gas. Anitrogen gas flow may be maintained for nitrogenation of the film.

[0069] The plasma beam source is capable of depositing ions with anenergy of between about 10 eV and 500 eV, while the optimal energy fordeposition of carbon is generally between about 80 and 120 eV per carbonatom. The hydrogen content may be between about 8 and 18 atomicpercentage, while dopant gases of between .7 atomic percent and 10atomic percent, typical dopant gases including N₂, or PH₃. Carbondeposition rates of between 2 and 12Å per second can be provided byplasma beam source deposition methods within the above operating ranges,ideally being between about 8 and 9 Å per second to provide the highestquality films. Deposition times of between about 6 and 30 seconds aregenerally used at these rates to provide a sufficient protective coatingfor magnetic recording media. In work in connection with the presentinvention, M. Weiler et al. describes the preparation and properties ofhighly tetrahedral hydrogenated amorphous carbon deposited using aplasma beam source in the journal Physical Review B, vol. 53, pp.1594-1608 (1996), the full disclosure of which is hereby incorporated byreference.

[0070] Although the plasma beam source deposition systems and methodsdescribed with reference to FIGS. 3A and 3D have several advantages,including the ability to accurately control the ion deposition energyand flux, these plasma beam sources do have some disadvantages. Oneprimary disadvantage of plasma beam source deposition is that thecapacitively coupled plasma density, and hence the deposition rate, isrelatively low. In order to increase the ion density, it would bebeneficial to provide higher pressures within the plasma confinementvolume, preferably maintaining the plasma at a pressure of 30 mTorr ormore. Unfortunately, the ionization coefficient tends to drop off atthese higher pressures, thereby limiting the total plasma density.Specifically, it will generally be advantageous to maintain lowdeposition pressures for at least two reasons. First, the proportion ofions in the particle stream decreases with increasing pressures.Basically, at higher operating pressures, gas scattering will reduce anddisperse the ion energy. In fact, deposition of highly tetrahedralamorphous carbon at pressures of over 30 mTorr when using the exemplarysystem is problematic, as films deposited at such pressures are formedprimarily with low energy radicals. Second, as pressures increase, theparticle flux increasingly includes varying particle masses (C₂, C₄, C₆,C₈ . . .). As uniform mass particles are preferred, plasma beamdeposition will preferably take place with pressures below lmTorr,ideally at a pressure of between about 0.1 and 0.5 MTorr. This, in turn,generally limits the deposition rates which may be achieved by plasmabeam sources and methods which rely solely on capacitative coupling tomaintain the plasma.

[0071] The hybrid beam source of the present invention maintains theadvantageous ion energy control of the plasma beam source, but provideshigher plasma densities and enhanced deposition rates without relying onincreases in pressure. Referring once again to FIGS. 2 and 2A, hybridsource 30 combines an inductive ionization system 32 with a capacitivecoupling system 36 (similar to that used in the plasma beam sourcesdescribed above) to provide a high density and low pressure plasma. Theinductive ionization system will again be explained in isolation, herewith referenced to FIGS. 4A and B.

[0072] Inductive ionization system 32 comprises an alternating powersource 90 capable of generating frequencies in roughly theradiofrequency-microwave range, preferably providing a potential with afrequency of about 27.12 MHz (or some multiple thereof). Once again, afrequency matching network 92 is provided, but the power is here coupledto the plasma using antenna 94 disposed around the plasma container 52.Advantageously, this minimizes any self-biasing of the plasma relativeto the antenna, and minimizes deposition of source materials onto thewalls of the container itself.

[0073] Plasma within an inductive discharge may be energized in anon-resonant or resonant inductive mode. Preferably, a small DC magneticfield is superimposed on the plasma volume to provide enhanced ionenergy transfer and plasma densification through a process which isgenerally described as resonant ionization.

[0074] Antenna 94 may be described as a dielectric wall around the axisof the plasma container. Alternatively, antenna 94l may be modeled as asingle loop inductive coil disposed about the plasma. Regardless, thepotential of the plasma with respect to the container surface remainslow, while the plasma density is quite high.

[0075] Typically, antenna 94 surrounds a cylindrical plasma containerhaving a length between one third and three times its diameter,preferably being of nearly equal length and diameter. The antennaconsists of a metal cylinder with a longitudinal slit. The superimposedstatic magnetic field B is generally normal to the axis of the plasmacylinder, and is applied by at least one magnetic coil 96 adjacent theplasma container. Resonant ionization potentials and magnetic fieldstrengths are more fully described by Professor Oechsner in PlasmaPhysics, vol. 15, pp. 835-844 (1974), the full disclosure of which isincorporated herein by reference.

[0076] The mechanism which will provide plasma densification willapparently be Electron Cyclotron Wave Resonance (ECWR), rather than therelated but different phenomenon of Electron Cyclotron Resonance (ECR).Both of these mechanisms can be understood with reference to thedispersion of an electromagnetic wave propagating parallel to a magneticfield, and more specifically, by analyzing the refraction index and thepropagating velocity (here being phase velocity Vp) as a function offrequency and magnetic field strength. We know that the refraction indexand propation velocity are related as follows:$\frac{\omega^{2}}{c^{2} \cdot k^{2}} = {\frac{v_{p}^{2}}{c^{2}} = \frac{1}{n^{2}}}$

[0077] where n is the refractive index, c is the speed of light, ω isthe frequency of the electromagnetic wave, and k is the magnitude of thepropagation vector for the electromagnetic wave. An ordinary wave can beexplained as a superposition of right- and left-handed circularlypolarized electromagnetic waves. In the case of a plasma, we should alsoconsider the different charges and masses of the electrons and ions.From the right- and left-hand polarized wave equations, we find aresonance effect is provided when ω is equal to the cyclotron frequencyω_(c) . Under these conditions, the refraction index goes to infinity,so that the propagation velocity is zero. This condition is referred toas ECR. Unfortunately, the wavelengths associated with ECR are generallylarger than the desired sizes of our plasma containers, so thatpractical application of ECR for plasma densification would bedifficult.

[0078] Fortunately, ECWR provides an alternative densification mechanismwhen ω is less than ω_(c). Neglecting the motion of ions due to theirmuch higher mass, the dispersion relation for the right-hand polarizedwave is approximated by:$n_{R}^{2} = {\frac{c^{2}k^{2}}{\omega^{2}} = {1 - \frac{\omega_{p}^{2}/\omega^{2}}{1 - \left( {\omega_{c}/\omega} \right)}}}$

[0079] ω_(p) is the plasma frequency. Generally, wave propagation ispossible when the phase velocity (and therefore the refractive index) ispositive. Schematic plots of the refractive index of a cold plasma andthe phase velocity of a cold plasma (both as a function of frequency)are given in FIGS. 4C and 4D. Examination of these plots reveals thatboth are positive below ω_(c). In fact, the refractive index for adriving potential having a frequency of 13.56 MHz will reach valuesabove 100. This means that wavelengths within the plasma may be reducedby +TE,fra 1/100 or more. If the wavelength can be reduced to thedimensions of the plasma container, it is possible to create standingwaves in the plasma which provide a resonant effect. This ECWR willdepend on the magnetic filed strength as well as the plasma containerdimensions. If our plasma container has a diameter a, this resonanteffect can generally be achieved if:$k_{r} = {\frac{2\pi}{\lambda} = {\frac{\pi}{a}\left( {{2\mu} + 1} \right)}}$

[0080] μ=1, 2, 3, . . . , λ is the wavelength, and k_(r) being theresonant magnetic field. The resonance can be tuned by varying therefractive index of the plasma. For ECWR, we will want to take intoaccount that the refractive index for the right-hand polarized wave willdepend on both the magnetic field and the plasma frequency. Thevariation of n_(r) with the plasma frequency complicates this tuningsomewhat, because the plasma frequency itself depends on the plasmadensity, which will, in turn, change with the degree of excitation ofthe plasma.

[0081] It is possibly to combine the densifying effects of inductiveionization on low pressure plasmas with the capacitive coupling ion beamextraction of the plasma beam source to greatly enhance depositionrates. Unfortunately, inductive ionization does not generally produce auniform plasma density. Hence, such a hybrid deposition system, withoutfurther modification, produces a non-uniform ion stream and depositionprocess. For these reasons, the present invention further provides aquasi-static resonant ionization magnetic field, as will be explainedwith reference to FIGS. 2 and 2A.

[0082] Referring once again to FIG. 2A, hybrid source 30 makes use of aplasma which is capacitively coupled so as to provide a stream of plasmaions through extraction grid 64. To promote effective capacitivecoupling, the plasma is maintained at a relatively low pressure,preferably below 1 mTorr. To enhance the density of the plasma, aninductive power transfer is locally achieved using antenna 94 ofinductive coupling system 32. The DC plasma potentially fromcapacitative coupling, and hence the ion acceleration energy, istypically about 20 to 40 volts at all surfaces. Advantageously, ionenergy can be selectively controlled by varying the DC bias of theextraction grid, as described above. A similar combination of inductiveand capacitative coupling was described for sputter treatment ofdielectric samples by Dieter Martin in a 1995 dissertation forUniversitat Kaiserslavtern, Fachbereich Physik, Germany. That referencemore fully explains the independent variation of ion energy and ioncurrent density, similar to that applied in the hybrid deposition systemof the present invention.

[0083] Ion/radical fluxes from hybrid source 30 may be enhanced usingthe inductive coupling system 32. To homogenize the ion stream producedby hybrid source 30, a slow moving resonant ionization magnetic field isapplied by quasi-static magnetic field generation system 34.

[0084] The preferred quasi-static magnetic field generation system makesuse of a plurality of coils 96 disposed radially about the plasmacontainment volume. Field rotator 100 selectively energizes coils 96 inopposed pairs, to apply a fairly uniform magnetic field throughout theplasma. The opposed coils are energized in the same direction, but onlybriefly, after which an alternate pair of transverse magnetic coils areenergized to apply a magnetic field B₂. Thereafter, the original coilsmay be reenergized, but with the opposite polarity so that magneticfield B₃, and then field B₄ are produced.

[0085] Field rotator 100 produces a magnetic field which effectivelyrotates through the plasma containment volume with a rotationalfrequency which is much less than the driving frequency of inductivecoupling system 32, generally being less than 10,000 Hz, and often beingless than 100 Hz. Thus, the rotating magnetic field provides resonantenhancement of the inductive coupling of a truly static resonant field.However, the rotation of the magnetic field densifies a much broaderregion of the plasma, and thereby provides a much more homogeneous ionstream. Moreover, the moving magnetic field may also further density theplasma by a churning effect, increasing the collisions between theenergetic plasma particles to provide still further increases indeposition rate and energy transfer efficiency.

[0086] A typical hybrid source will have a container volume with aninternal radius of about 5 cm, and a length between the couplingelectrode and the extraction grid of about 8½ cm. Such a hybrid sourcewill require an ionizing energy of between about 100 and 1000 watts,when driven at a frequency of about 13.56 MHz (or some multiplethereof). Clearly, a wide variety of alternative container geometriesand sizes may be provided, within the scope of the present invention.

[0087] When using hybrid source 30 for deposition or etching, the plasmacontainer and deposition vessel surrounding the substrate are evacuated,preferably at a relatively high speed of about 2,000 liters per second.The ambient pressure during deposition will preferably be kept at about5×10 ⁻⁴ mbar. Once again, a short burst of N₂ gas is superimposed on asteady flow of the source gas to facilitate striking of the plasma, anda gas comprising nitrogen may be continuously supplied wherenitrogenation is desired. A burst on the order of a few millisecondswill suffice, or, alternatively, a high voltage pulse striker circuitmay be used with similar results. Ion current densities aresubstantially higher than the 0.0 1 to 0.07 mA/cm² provided by plasmabeam sources, and may provide carbon deposition rates of between about20 to 100 Å per second.

[0088] Although hybrid source 30 is a preferred embodiment, a widevariety of alternative systems may also be used. For example, the movingmagnetic field may be provided by mechanically rotating one or morecoils about the plasma containment volume.

[0089] A still further alternative deposition system will be describedwith reference to FIG. 5. As illustrated, magnetic disk 2 issimultaneously coated on both sides by a pair of filtered cathodic arcsources 100. Each cathodic arc source includes a high density carbontarget 102 which is used as a cathode. Here, a plasma is maintained byan electrical potential of the cathode relative to a graphite extractoranode 104 once the chamber has been evacuated through evacuation port106. Generally, cathodic arc deposition relies on a low voltagedischarge at pressures of less than 10⁻⁵ mbar. Vaporized electrodematerial in the form of highly ionized intraelectrode plasma providescurrent transport between the cathode and anode. Typically, the solidcathode is consumed through microscopic localized regions of very highcurrent density and temperature, the cathode typically being anelectrically conductive deposition material such as a metal, carbon, orhighly doped semiconductor. Advantageously, the kinetic energy of ionscan be electrostatically varied by biasing the substrate relative to thecathode. Energetic bombardment of the film using cathodic arc source 100can produce dense and continuous films through subplantation, asdescribed above. High deposition rates of between 30 and 100 Å persecond, together with high throwing power (the ability to coat uniformlyin three dimensions) are also provided by the intense ion flux.

[0090] To initiate the arc, piezo system 108 passes through the wall ofthe deposition chamber using a linear and rotary feedthrough 110 so asto initially energize a graphite striker 112. Water cooling 114 helpsconfine the discharged energy to the deposition system.

[0091] Unfortunately, cathodic arc systems suffer from the expulsion ofmacroparticles (together with the plasma) from the surface of thecathode. The inclusion of these macroparticles can seriously limit thequality of films grown on substrates placed in front of the cathode.Therefore, source 100 blocks the direct path between the cathode and themagnetic recording media or other substrate to be coded using acurvilinear duct 116. Magnetic field coils 118 direct the desiredparticles through curvilinear duct 116, effectively filtering out themajority of the macroparticles. The use of baffles 120, and an irregularduct surface formed by bellows 122, helps to prevent the macroparticlesfrom bouncing along the curvilinear duct, thereby providing a moreeffective filter. The duct will typically be about 7.3 inches indiameter, while the curve may have a centerline radius of about teninches.

[0092] The filtered ion stream may be optionally accelerated towards thesubstrate using an acceleration grid 124. Alternatively, the substrateitself may be biased. To provide a more uniform deposition process, thefiltered ion stream may also be scanned over the substrate surface usinga raster magnetic field supplied by raster coils 126. Optionally, theion stream may be monitored through viewport 128. Steering magneticfields may also be provided at the cathode by steering coils 129.

[0093] It would be advantageous to minimize the macroparticles ejectedfrom the cathode, rather than relying entirely on filtering. Toward thatend, the present invention provides cathodes which are adapted todistribute an arc over a diffuse cathodic surface area, rather thanforming a number of discrete arc spots or jets. To provide such adistributed cathodic arc over an active region 130 of cathodic source102, the power per unit area is generally raised to a sufficient levelfor the active region to reach a critical temperature.

[0094] Cathodic arc deposition of graphite is particularly problematic,as graphite in general is difficult to evaporate or sublime byelectrical heating, largely because of its anomalous negativetemperature coefficient of electrical resistivity (up to about 1,200°K).

[0095] Graphite is generally porous in nature, leading to largequantities of macroparticles being ejected during arcing. While thecurvilinear duct filter described above has proven effective at limitingthe amount of macroparticles reaching the substrate, this structure alsoproduces a magnetic pinching of the plasma stream, which reduces thearea of deposition and tends to produce inhomogeneity in the thicknessof the deposited films. Additionally, over a long period of time, thecontamination of the filter duct walls can be disadvantageous, ascharged carbon dust from the wall may become entrapped in the plasmastream and contaminate the film.

[0096] To reduce macroparticle content from a graphite target, thetemperature of the cathode at or near the surface is increased to atemperature above the minimum point in the resistivity versustemperature curve for various types of graphite. Ideally, thetemperature will be raised substantially beyond this minimum resistivitytemperature to enhance ohmic heating and thus evaporate the graphitemore effectively. To provide a more stable process, it is generallyadvantageous to make use of a direct current cathodic arc, in which thearc itself can have a overall lifetime of minutes, unlike spot ortransient arcs which can appear and dissipate across the surface of thecathode within a time span on the order of a few nanoseconds. The goalhere is to enhance the effect of local heat accumulation at the surfaceof the cathode, and to promote this heat trapping process on a timescale which is significantly longer than that of known arc depositionsystems. Work in connection with the present invention has shown thatcontinuous DC arcs may be produced with durations of over 1 minute andpreferably of over 3 minutes.

[0097] Energy conservation at the cathode implies that the energy inputand energy output are equal. Energy is generally supplied to the cathodesurface through ohmic heating, ion bombardment, and Nottingham heating.Energy will be lost during the process through electron emissioncooling, evaporation cooling, and heat transfer by conduction,radiation, and convection.

[0098] The carbon cathode itself may optionally be prepared bycompressing high purity graphite powder at a hydrostatic pressure ofbetween about 130 and 150 MPa. The density of such a cathode willtypically be between about 1.5 and 1.7 g/cm³. To enhance the heattrapping at the cathode surface, the cathode can be thermally insulatedwith thermal insulation 132.

[0099] When the arc is first struck, the cathodic discharge evolves as avisible microscopic dot with a plasma ball, similar in appearance toknown cathode vacuum arcs. At the initial stage of arc triggering, thearc voltage is about 20 volts, which is typical of spot arcs for thesame arc current. Sometime after ignition, however, the single cathodicspot will evolve into a diffuse active area, preferably being at least 2cm². Ideally, the surface temperature within that area reaches a valuenearing the sublimation temperature of graphite, often being over 2,000°C. The steady state distributed arc mode may be characterized by a meanarc voltage value that fluctuates over about 25 volts, ideally beingbetween about 30 and 33 volts. The imposition of a steering magneticfield may decrease the transition time from the spot mode to thedistributed arc mode.

[0100] A reduction in macroparticle content may be visible observed as areduction of the number of incandescent particles within the plasma ascompared to the standard spot arc. A diffuse plasma cloud is formed overthe cathode surface, and the wide amplitude fluctuations characteristicof the spot arc are reduced. Additionally, the audible rattling noiseoften provided by filter cathodic arcs is replaced by a notably quietererosion process. Erosions of 2 mg/s have been measured over a series ofruns accumulating a total of 5 minutes of arcing.

[0101] Rise in the cathodic temperature may conveniently be produced bythe reverse ion bombardment and Joule heating of cathode 102. Thermalinsulation 132 may also prevent dissipation of the heat energy tocooling water system 114. Thermal insulation may be disposed over aselected portion of cathode 102 so as to selectively control the sizeand position of active region 130.

[0102] The distributed cathodic arc of the present invention produces asignificantly lower total current density and a higher spatialuniformity in ion current density. Such a distributed arc may make useof a higher arc voltage than in the more conventional cold cathodic arcsources, as well as a reduced amplitude in arc current oscillations,which will help to decrease the macroparticle content of the associatedplasma. Reduction of macroparticles will reduce cleaning and maintenanceof a filter duct, and may even allow unfiltered deposition. Unfilteredcarbon distributed arc films may be produced having densities of over 3g/cm³ with a mean ion energy of 18 eV, at over 50 Å/s, by a particleflux with an ionization of over about 60%.

Experimental

[0103] Films were deposited on aluminum substrates over a magnetic layerusing opposed plasma beam sources and acetylene plasmas. The depositionconditions are summarized in Table 1. These conditions gave a highlyionized plasma and an ion beam energy of about 120 eV/C ion within awell-defined energy window. TABLE I Item A-side B-side Conditionrf-input power 250 W 250 W Phase-matched rf- reflected 5 ± 1 W 7 ± 1 WStable during deposition power Inner Coil 7.0 Å 7.0 Å Current Outer Coil−0.5 Å −0.5 Å Reverse Polarity Current Gas-flow rate 18 sccm 18 sccmPlasma ignited at 43 sccm with a burst of N₂ gas Dep-Rate 8-9 Å/s 8-9Å/s Deposition time varied from 10-30 s

[0104] The acetylene gas flow rate was pre-set (by an electroniccontroller) to promote diamond-like bonding in the ta-C:H carbon films,rather than optimizing the deposition rate. Gas flow rates are instandard cubic centimeters per second (sccm). The matching-networkcircuit passive elements were pre-tuned so as to minimize the ratio ofP_(ref)/P_(in) (power reflected over power input) at the above-mentionedacetylene flow rate.

[0105] The rate phase state was triggered using a short burst of N₂ gas(lasting less than 0.1 s) superimposed on the steady flow of C₂H₂. Thepressure of the chamber during deposition was in the region of 5 ^(*) 10⁻⁴ mbar. Textured and untextured smooth disks were coated, and thecarbon coatings were characterized using ellipsometry, electron energyloss spectroscopy (EELS) and Raman finger-printing. The textured diskswere lubed using conventional lube processes, and underwent abrasivetape tests as well as accelerated start-stop tests.

[0106] Table II summarizes the variation of physical properties of thefilms as a function of thickness. The average ion energy per carbon ionwas uniformly maintained at about 100 eV. The spatial homogeneity of thefilms is gauged in both the radial as well as angular positions.Generally, G-peak and D-peak are V-peak positions in Raman spectroscopy,while the associated Δ values describe peak widths. Selket voltage isthe output voltage of a light sensor for abrasive wear test equipmentmanufactured by Selket Co. The higher the output voltage, the moreserious the wear. TABLE II thickness Selket Voltage RMS* R_(a) RamanPlasmon Peak Item (A) ± 10 (mV) G-peak ± 5 cm⁻¹ G-peak_(—) ± 5 cm⁻¹(Angs) I_(d)/I_(g) (eV) Cell 1 40 3 1494 150 3 0.24 31.4 Cell 2 50 21498 152 4 0.48 30.0 Cell 3 70 5 1508 138 6 0.5 29.5 Cell 4 80 7 1507137 6 0.6 29.8 Cell 5 100 6 1509 130 9 0.7 29.7 Cell 6 200 7 1509 130 81.0 25.5

[0107] One noteworthy observation from the Raman spectra is the increasein both the position of the G-peak as well as the I_(d)/I_(g) ratio (thearea ratio of the D and G peaks) with increasing film thickness. Thisshows that the percentage of C-C sp³ content in the bulk of the filmsincreases with decreasing thickness. D-peak bandwidth also increaseswith decreasing film thickness within the range monitored. The bandwidthof the D-peak in the optimized films is above 150 cm⁻¹, indicating verylow levels (or absence) of graphitic phase clustering within thediamond-like carbon amorphous matrix. This result is consistent with therelatively high Plasmon-peak measured from theelectron-energy-loss-spectroscopy (EELS). Plasmon peak is the energy ofa type of excitation called a plasmon. It is a quantum of chargedparticle cloud vibration. The energy value is directly related to thecharged particle (e.g., electron) density.

[0108] The Plasmon-peak E_(p) is representative of the density of thefilms. Thus, taking the E_(p) of diamond to be 34 eV, it is estimatedthat the most-diamond-like ta-C:H films have above 80% C-C sp³ bonding(this is independent of whether there is long range order or not).

[0109] Disks were coated with ta-C:H films under a wide variety ofrf-power and gas-feedstock flow rates. These films were then tested forfriction build-up and wear durability using a conventional acceleratedcontact start/stop (CSS) test. Prior to testing, the disks were lubedand lube thickness was found to vary between 16-23 Å, corresponding to acarbon film thickness range of 30 Åto 150 Å. Each test consisted of 500cycles, and the disks were tested on both sides at 300 rpm. The averagedcoefficients of friction (μ_(s)) are plotted against thickness of thefilms in Table III. The variation of μ_(s) is found to be between 0.5 to1.5, corresponding to a thickness range from 40 Å to 150 Å. Of the 16disks that underwent the accelerated CCS test, all but one passed. TABLEIII rf power Gas flow-rate Coefficient of static (Watts) (sccm)Deposition time(s) friction μ_(s) 500 20 10 1.6 100 12 30 1.8 500 20 61.5 100 20 6 1.6 300 16 6 1.4 500 20 6 1.5 500 20 30 2.0 500 20 12 1.5500 20 6 1.9 100 12 6 1.7 100 12 6 1.6 100 12 30 1.6 100 16 18 1.5 30016 6 1.3

[0110] Disks were also coated with highly tetrahedral amorphous carbonusing a filtered cathodic arc. Initially, two disks were coated with astatic ion stream, producing coatings which varied considerably from thecenter to the edge. Estimating coating thicknesses using interferencecolors, and assuming an index of refraction of 2.5, coating thicknessesvaried at least between 1,250 Å and 500 Å.

[0111] Raw data from Selket abrader tests are provided in FIGS. 6A andB. Over the two 120 second tests, no debris was seen on the tape. Only avery faint wear track was found after tests were complete.

[0112] Peak friction of the disks was also measured as a function of thenumber of start/stop cycles. The results of these tests are provided inFIG. 7.

[0113] The Raman spectra of the filtered cathodic arc disks were alsomeasured, and the ided in FIG. 8. Generally, these results indicate thata film can be deposited using a cathodic arc source which includes aG-peak in the area of about 1518, and having a G width of approximately175. The pseudo band gap of this film appears to be roughly 1.68 eV,while the refractive index is approximately 2.5. The complex portion ofthe optical index of refraction, K, appears to be approximately 0.08 forthe film.

[0114] An additional disk was coated, this time on both sides, using afiltered cathodic arc source. The ion stream was swept over the surfaceof the substrate by manipulating permanent magnets placed on either sideof the chamber. No bias was applied to the scanned substrate. Althoughthe scanning mechanism here was quite simple, a more uniform depositionlayer was provided.

[0115] Although the foregoing invention has been described in somedetail, by way of illustration and example, for purposes of clarity ofunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the appended claims.

What is claimed is:
 1. A system comprising: a magnetic recording mediahaving a protective coating comprising a highly tetrahedral amorphouscarbon having a smoothness which increases as a thickness of the coatingdecreases; and a read/write head.
 2. A system as in claim 1, wherein anareal recording density of the recording media is over 1 gigabyte persquare inch.
 3. A system as in claim 1, wherein the read/write head hasa glide height less than about 1μ″.
 4. A system as in claim 1, whereinthe protective coating is adapted for use with near-contact of therecording media with the read/write head.
 5. A system as in claim 1,wherein the protective coating is adapted for use during continuouscontact of the recording media with the read/write head.
 6. A system asin claim 1, wherein the thickness of the protective coating is in therange between about 30 Å and 70 Å.
 7. A system as in claim 1, whereinthe read/write head has a protective coating comprising a highlytetrahedral amorphous carbon.
 8. A system comprising: a magneticrecording media having a protective coating comprising a highlytetrahedral amorphous carbon having more than about 70% sp³ carboncarbon bonds; and a read/write head; wherein the coating has a thicknessof less than about 40 Å; wherein the coating has a hardness of overabout 80 GPa.
 9. A magnetic read/write head having a protective coatingcomprising: a highly tetrahedral amorphous carbon.
 10. A magneticrecording media for use with a read/write head, the media comprising: asubstrate; a magnetic layer disposed over the substrate; and aprotective layer over the magnetic layer, the protective layercomprising a highly tetrahedral amorphous carbon; wherein the protectivelayer has a thickness of less than about 50 Å and a hardness of overabout 80 GPa; wherein the protective coating is adapted for use duringcontinuous contact of the media with the read/write head; and whereinthe media has an areal density of over 1 gigabyte per square inch.
 11. Amethod for depositing a protective coating comprising a continuoushighly tetrahedral amorphous carbon on a substrate, the methodcomprising: ionizing a source material so as to form a plasma containingions which comprise carbon; and energizing the ions to form a streamfrom the plasma toward the substrate so that carbon from the ions isdeposited on the substrate, wherein the ions impact with an energy whichpromotes formation of sp³ carbon carbon bonds.
 12. A method as in claim11, wherein the carbon is deposited on the substrate at a rate higherthan about 10 Å per second.
 13. A method as in claim 11, wherein thesource material comprises acetylene.
 14. A method as in claim 11,wherein the substrate comprises at least one of magnetic recordingmedia, glass, optics, machine tools, and integrated circuits.